Overview
This lecture introduces leukocytosis (increased white blood cell count), its causes, interpretation, and associated clinical actions.
Basics of Leukocytosis and WBC Count
- Leukocytosis is defined as WBC count >11 x 10⁹/L.
- Normal WBC range: 4.5–11 x 10⁹/L per liter.
- Trends in WBC are important; rising counts may indicate worsening process, while falling counts may indicate resolution.
- WBCs (white blood cells) include neutrophils (bands, segs), lymphocytes, monocytes, and eosinophils.
WBC Differential and Interpretation
- Neutrophils (bands & segs): increased in bacterial (pyogenic) infections.
- Lymphocytes: increased in viral infections and sometimes tuberculosis.
- Monocytes: elevated in tuberculosis and some viral infections.
- Eosinophils: elevated in allergies, parasitic infections, and coccidioidomycosis (fungal infection).
- Normal differential: Segs/Bands ~60%, Lymphocytes ~20%, Monocytes ~5%, Eosinophils ~2-4%.
- Deviations from normal suggest specific diseases (e.g., high eosinophils = allergy/parasite).
Main Causes of Leukocytosis
- Four main causes: Infection, Steroids, Cancer/Leukemia, Catastrophic Event.
- Infection: Look for fever, pain, and "left shift" (increased bands).
- Steroids: Cause leukocytosis via demargination (60%), delayed migration (30%), minor band release (10%).
- Leukemia/Lymphoma: Malignant proliferation or decreased cell death; confirmed with abnormal smear, pathologist review, and possibly bone marrow biopsy.
- Catastrophic Event: MI, cardiac arrest, major PE, or surgery cause transient WBC elevation.
Clinical Approach to Leukocytosis
- For infection: Look for fever, symptoms, and positive diagnostic tests (CXR, urinalysis, CT, lumbar puncture).
- In steroid-related cases: WBC rises proportionally without significant band increase.
- Markedly high WBC (>30-50 x 10⁹/L): Consider Clostridium difficile colitis, especially in hospitalized patients.
Key Terms & Definitions
- Leukocytosis — increased white blood cell count (>11 x 10⁹/L).
- Bands — immature neutrophils; rise in bacterial infection.
- Segs (Segmented neutrophils) — mature neutrophils.
- Left shift — increased bands, indicating acute infection.
- Demargination — movement of WBCs from vessel wall to bloodstream (seen with steroids).
- Leukocyte alkaline phosphatase (LAP) score — measures enzyme in WBCs; low in leukemia, high in infection.
Action Items / Next Steps
- Review WBC trends and differential in clinical cases.
- Be alert for signs of infection, especially with very high WBC.
- Order appropriate tests (CXR, urinalysis, CT, LP) based on symptoms.
- Consider further workup (smear, pathology, bone marrow) if suspicion for malignancy.
- Read about common infections and causes of leukocytosis.